Podcast
Questions and Answers
Which memory segment is also known as the 'free store'?
Which memory segment is also known as the 'free store'?
- Data Segment
- BSS Segment
- Heap Segment (correct)
- Code Segment
The code segment typically contains read-only executable instructions.
The code segment typically contains read-only executable instructions.
True (A)
What is a LIFO data structure?
What is a LIFO data structure?
Last-In, First-Out
The _________ segment contains uninitialized global and static variables.
The _________ segment contains uninitialized global and static variables.
Match the memory allocation type with its description:
Match the memory allocation type with its description:
Which of the following is a characteristic of static memory allocation in C++?
Which of the following is a characteristic of static memory allocation in C++?
Static variables are allocated on the stack.
Static variables are allocated on the stack.
What is the primary function of the call stack?
What is the primary function of the call stack?
When a function is called, a ______ ______ is created and pushed onto the stack.
When a function is called, a ______ ______ is created and pushed onto the stack.
Match the stack operation with its description:
Match the stack operation with its description:
What is a key advantage of using the stack for memory allocation?
What is a key advantage of using the stack for memory allocation?
Variables stored on the stack can be resized during runtime.
Variables stored on the stack can be resized during runtime.
What does a stack pointer register track?
What does a stack pointer register track?
The heap is managed by the ______.
The heap is managed by the ______.
Match the memory function with its description:
Match the memory function with its description:
What is a potential problem when allocating a very large block on the heap?
What is a potential problem when allocating a very large block on the heap?
Memory allocated on the heap must be explicitly deallocated by the program.
Memory allocated on the heap must be explicitly deallocated by the program.
What is the purpose of memset()?
What is the purpose of memset()?
The ___________ function copies memory from one block to another.
The ___________ function copies memory from one block to another.
Match the function with its proper use case:
Match the function with its proper use case:
Which function allocates memory and initializes it to zero in a single step?
Which function allocates memory and initializes it to zero in a single step?
It’s acceptable for a C program to never call free() to deallocate memory.
It’s acceptable for a C program to never call free() to deallocate memory.
What happens if a pointer to allocated memory is lost and can no longer be referenced?
What happens if a pointer to allocated memory is lost and can no longer be referenced?
Failing to check the return value of malloc() can lead to a ________ ______ if the allocation fails.
Failing to check the return value of malloc() can lead to a ________ ______ if the allocation fails.
Match the description of common issues with C/C++ memory operations:
Match the description of common issues with C/C++ memory operations:
Suppose you have a dynamically allocated array using malloc(). Which function should you use to increase its size?
Suppose you have a dynamically allocated array using malloc(). Which function should you use to increase its size?
It is safe to access memory after it has been freed using free().
It is safe to access memory after it has been freed using free().
What is heap fragmentation and why is it a problem?
What is heap fragmentation and why is it a problem?
The _______ is automatically adjusted each time a value is pushed onto or popped from the stack.
The _______ is automatically adjusted each time a value is pushed onto or popped from the stack.
Where are static variables stored if they are uninitialized?
Where are static variables stored if they are uninitialized?
Stack operations are slower than heap operations.
Stack operations are slower than heap operations.
What does LIFO stand for?
What does LIFO stand for?
Variables allocated automatic memory will be freed when the relevant code block is _________.
Variables allocated automatic memory will be freed when the relevant code block is _________.
Why is it generally bad practice to allocate large arrays on the stack?
Why is it generally bad practice to allocate large arrays on the stack?
The call stack primarily keeps track of inactive functions.
The call stack primarily keeps track of inactive functions.
What does a program do once the function terminates?
What does a program do once the function terminates?
The BSS segment is also known as ___________ data.
The BSS segment is also known as ___________ data.
What is the danger of returning *ptrA in given code? TestClass *ptrA = &objTC;
What is the danger of returning *ptrA in given code? TestClass *ptrA = &objTC;
You can initialize global variables inside the header file.
You can initialize global variables inside the header file.
If an allocation fails, what will malloc return?
If an allocation fails, what will malloc return?
Make sure you __________ memory allocated dynamically.
Make sure you __________ memory allocated dynamically.
Flashcards
Code Segment
Code Segment
A memory area also known as the text segment.
BSS Segment
BSS Segment
A memory area also known as uninitialized data.
Data Segment
Data Segment
A memory area adjacent to the BSS segment.
Heap Segment
Heap Segment
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Call Stack
Call Stack
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Static Memory Allocation
Static Memory Allocation
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Automatic Memory Allocation
Automatic Memory Allocation
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Dynamic Memory Allocation
Dynamic Memory Allocation
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LIFO Structure
LIFO Structure
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Stack Frame
Stack Frame
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Stack Advantages
Stack Advantages
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Stack Disadvantages
Stack Disadvantages
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Heap
Heap
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Heap Fragmentation
Heap Fragmentation
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malloc
malloc
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calloc
calloc
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realloc
realloc
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memset
memset
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memcpy
memcpy
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strdup
strdup
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free
free
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void free(void * ptr)
void free(void * ptr)
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void *malloc(int size)
void *malloc(int size)
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C Commandments
C Commandments
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Closest Points
Closest Points
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Study Notes
- The lecture covers memory allocation strategies, focusing on the stack versus the heap
Program Memory Segments
- Code Segment: Also known as the text segment, contains program's executable instructions, and is read-only
- BSS Segment: Contains all uninitialized (or initialized to 0) global and static variables
- Data Segment: Adjacent to the BSS, it contains initialized static variables, size determined by data types in source code, and doesn't change at runtime
- Heap Segment: Also called the free store, for dynamically allocated variables
- Call Stack: Simply called stack which is a LIFO structure that tracks function calls
Call Stack Details
- A stack pointer register tracks the top of the stack, adjusting as values are pushed or popped
- Function parameters, local variables, and related information are stored here
Memory Allocation Types in C++
- Static Memory Allocation: For static and global variables, allocated once at program start and persists throughout life
- Automatic Memory Allocation: For local variables and function parameters; allocated upon code block entry and freed upon exit
- Dynamic Memory Allocation: Used when memory is needed, and the memory must be explicitly freed when done
Static vs Automatic Allocation
- Size of variable/array must be known at compile time
- Memory allocation and deallocation is automatic
Static vs Automatic Variables
- Static variables are allocated in BSS (uninitialized) or Data Segment (initialized) and is not on the stack
- Automatic variables are allocated on the stack and persist only during a single function call
The Call Stack
- Call stack keeps track of active functions, allocating function parameters and local variables, implemented as a container with peek(), top(), pop() and push()
- A stack frame stores function call data and a stack pointer tracks the top of the call stack
The Call Stack's Operation
- When program encounters a function call, a stack frame containing the return address, function arguments, local variables, and register values gets pushed onto the stack
- The CPU jumps to the function's start point
- Upon function termination, registers are restored, the stack frame is removed (freeing memory), and the CPU resumes execution at the return address
Advantages and Disadvantages of the Call Stack
- Advantages: Fast stack operations, memory size known at compile time, automatic memory management, contiguous memory
- Disadvantages: Relatively small size (typically 1MB on Windows, up to 8MB on Linux), may waste allocated memory, variables cannot be resized, LIFO access only
The Heap
- Heap is a larger memory pool managed by the OS
- Heap Memory is dynamically allocated to variables that returns to the OS once the program is done using it
- The program is responsible for allocation/deallocation by creating blocks of suitable size, and can fail if blocks are not of a large enough size (heap fragmentation)
Common Memory Allocation Functions
malloc: Allocates memory without initializingcalloc: Allocates memory and initializes to 0realloc: Resizes previously allocated memorymemset: Fills memory with valuememcpy: Copies memory block to anotherstrdup: Duplicates a string with null-terminationfree: Frees allocated memory
Memory Management Details
void free(void * ptr): Takes a pointer to allocated memory and returns it to the heap- Once memory is freed, it should not be accessed unless reallocated, and undefined behavior results otherwise
- Important:* When a program ends, its memory is completely freed
- Uncommon for some programs to never free memory while running in general
- Use calloc() to allocate and initialize in one go.
malloc Details.
void *malloc(int size): Takes a positive integer and returns a pointer if successful, or NULL if not- The memory is uninitialized and contains anything
- It is good practice to initialize the memory to all zeros, using memset()
Proper C Coding Rules
- Do not put variable definitions in header files because the same code will appear in multiple code files, cauing the linker to complain of multiple definitions of the same symbol.
- Every code file, except the one containing main() should have a corresponding header file.
- All functions and variables that are used outside of a code file should be declared (not defined) in the corresponding header file.
- Initialize all variables, particularly pointers. Do not utilize global variables unless required by an API.
- Confirm the
malloc()return value - Initialize memory following allocation.
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Description
Explore memory allocation strategies with a focus on the stack and heap. Covers program memory segments like code, BSS, and data. Details the call stack's role in tracking function calls and dives into static memory allocation in C++.
